Measuring system



April 21, 1953 A. J. HORNFECK 2,636,151

MEASURING SYSTEM Filed Jan. 51, 1952 4 Sheets-Sheet l FIG. I

INVENTOR. ANTHONY J. HORNFECK BY iv iw April 1953 A. J. HORNFECK 2,636,151

MEASURING SYSTEM Filed Jan. 31. 1952 4 Sheets-Sheet 2 H AMPLIFIER :6?

AND MOTOR CONTROL FIG. 2

: 5 i 79 78 I9 I l 66 82 72 7 w 65 8| O 'b l l 1' H 38 AMPLIFIER AND MOTOR CONTROL INVENTOR. 3 ANTHONY J. HORNFECK BY (Ml J.

ATT A/EV April 21, 1953 A. J. HORNFECK MEASURING SYSTEM 4 sheets-sheet 5 Filed Jan. 31. 1952 INVENTOR.

ANTHONY J HORNFECK Apriil 21, 1953 A. J. HORNFECK MEASURING SYSTEM 4 Sheets-Sheet 4 Filed Jan. 31. 1952 K .m mm m m J. R W wA J N m A V. fl

FIG. 6

Patented Apr. 21, 1953 MEASURING SYSTEM Anthony J. Hornfeck, South Euclid, Ohio, as-

signor to Bailey Meter Company, a corporation of Delaware Application January 31, 1952, Serial No. 269,274

9 Claims. I

This invention relates to electric calculating systems, and more particularly to systemswhich are adapted to indicate or record a product of variables such asquantlties, qualities, conditions,

.or the like.

This invention further relates to novel forms of movable core transformers having a plurality transformers is found in the control of their variable outputs to balance the variable output ora responsive device while their constant output supplies the basic energization of the responsive device. The flexibility of these movable core transformers enables balanceable networks to 1 attain a high degree of efficiency in performance and economy in the number and size of transformer-type of devices required.

A preferred form of my invention may include a balanceable network which is sensitive to variables and which operates when unbalanced to effect an actuation of a device for rebalancing the network. The unbalancing of the network may be producedby moving one or more adjustable members which are so interrelated as to eiiect Ian unbalance proportional to the product of values represented by positions of the members.

If desired, each of the members may be positioned in response to some variable or only one of the members may be positioned inresponse to a variable while another member is positioned manually to establish a factor by which the variable is to be multiplied.

Another form of my invention may include a balanceable network in which an unbalance may be produced by the inherent sensitivity of one ofthe included devices to the variable. One of these included devices may take the form of a Wheatstone bridge having a temperature sensithe leg and having its energizing potential supplied from the constant potential of the dualpurpose movable core transformer. In any event,

the balanceable networks, in which my dual-purpose movable core transformer is useful, are not restricted to networks including devices mechanically actuated in accordance with variables.

An object of my invention is to provide an improved calculating system. Another object is to provide an improved electrical system for indicating the product of a plurality of values. Still another object is to provide an improved calculating system having a balanceable network and means for producing an unbalance of the system in proportion to the product of variables.

Other objects of my invention are found in the provision of a movable core transformer with a plurality of outputs. Still another object is to provide a combination of potential producing devices with the dual-purpose transformer for performing calculations or single element measuring functions with an efficiency and economy not heretofore attainable with conventional combinations.

In the accompanying drawings there are shown for purposes of illustration several forms which my invention may assume in practice. In these drawings:

Fig. l is a schematic diagram of a system for indicating the product of the rate of flow and pressure in a fluid conducting conduit.

Figs, 2 and 3 are schematic diagrams of other systems for indicating products of variables.

Fig. 4 is a schematic diagram of a system for indicating the product of the rate of flow and pressure in a fluid conducting conduit when balanced by my novel form of movable core transformer.

Fig. 5 is a schematic diagram of another system for indicating a product of temperature and flow in a fluid conducting conduit when balanced by my novel form of movable core transformer.

. Fig. 6 is a schematic diagram of a system for indicating temperature of a condition by a bridge supplied and balanced by my transformer.

Referring to the drawings it will be noted that there is shown in Fig. 1 a system for indicating the product of the rate of fluid flow and pressure in a conduit I. The rate of flow is determined by a flow meter, generally designated 3, comprising a U-tube having legs 4 and 5 connected at one end in communication with the conduit at opposite sides of an orifice plate 6, and joined at their opposite ends by a tube 8. A liquid, such as mercury, partially fills the legs of the U-tube and is subjected to the pressures in the conduit at opposite sides of the plate 13. On the surface of the liquid in leg 3 is a float it, which is adapted to position a magnetic member ll within a leg portion l2 made of non-magnetic material. The member H acts as the core of a transformer which has a primary winding 15, a secondary winding l5, and a pair of secondary windings I1, [8 connected in series bucking. The primary winding is connected by conductors 20 and 2| to a source of alternating current and is magnetically coupled by the member i l to the secondary windings. The ends of the secondary winding are connected by conductors 22 and 23 to the ends of a potentiometer 24, and the remote ends of the windings l1, l8 are connected by conductors 25, 26 to the ends of a potentiometer 21.

The core member i l is so arranged as to effect a constant induced potential E1 in the secondary winding [6 for any position that it may assume during variations in the flow of fluid through con-' duit I. At a predetermined rate of fluid flow, the member l I assumes a central position relative to the secondary windings ll, [8, and the result ant induced potential in these windings is then equal to zero. A movement of the core member L from its central position results in an increase in the potential induced in one of the windings ll, l8, and a decrease in the potential induced in the other winding. The resultant potential across these windings will then be equal to some value E2 which is dependent upon the distance at which the core member is spaced from its neutral position.

The potentiometers 24, 21 are connected together at one end by a conductor 30 and are provided with movable contacts 3i and 32 respectively connected by conductors 33 and 34 to an amplifier 35. The circuit including the secondary windings l6, I1, 18, the potentiometers 24, 2'1,

and the conductors 3t, 33, 34 comprises a balance-' able network of the null type. The movable contact 32 is shown herein connected to a Bourdon tube 35 which is responsive to pressures in the conduit I, and the contact 3! is operatively connected to a motor 38 for adjustment by the latter. A motor control circuit 40 is adapted to be energized by the amplifierwhen the network becomes unbalanced and effects an operation of the motor in a direction to rebalance the network.

The connections between the amplifier and the potentiometers 24, 2'! are such that the potentials acrOss the portions of the potentiometers between the conductor 30 and the movable contacts oppose each other in determining the potential applied to the amplifier. The potential across the portion of the potentiometer 27, represented by E3, will be seen to vary directly with the potential E2 as well as with the movement of the contact 32. Since the potentiometer '24 is subjected to a constant potential E1, the potential E4 between theconductor 30 and the contact 3! will vary only with the movement of the contact and will be equal to the potential E3 when the network is balanced.

A change in the rate of fluid flow or a change in pressure in conduit l causes the potential E3 to vary and establish a potential E5 which is subjected on the grid 42 of a double triode tube 43 in the amplifier circuit. A resistance 44 connected in the output circuit of the amplifier has a potential across it varying with the potential on the grid 42.

The motor control circuit to includes tubes 45 and 4'! having their anodes connected respectively through windings of saturable core reactors 48 44, and the tube grids are connected to a movable contact 5| for the resistance 44. The primary winding of the power transformer is connected to an A. C. power line by conductors 52 and 53. It will be seen that with one phase output of the amplifier 35, the tube 45 will be made conductive at such a time that current may flow from the secondary of the power transformer during one half cycle through the winding of the saturable core reactor 43 and the tube back to the transformer. During the other half of the cycle, the tube 47 will become non-conductive and no current will flow in the motor control circuit. When the phase output of the amplifier reverses, the tube 4'! becomes conductive at the proper time to permit current to flow during one-half cycle from the power transformer through the saturable core reactor 49, and the tube 46 becomes non-conductive during the other half cycle to prevent current flow at such time.

The circuit vfor the motor 38 includes stator windings 54 and 55 connected atadjacent ends through a' conductor 56 to one'side of the power line and connected at their opposite ends to wind ings of the saturable core reactors 48 and 49'. Connected between the remote ends of the motor windings and 55 is a condenser 58. The-ends of the saturable core reactor windings remote from the motor windings are connected through the primary of the transformer 50 and the conductor 53 to the side of the power line opposite from the conductor 56. 7

When the portion of the motor control circuit including the reactor 48 and the tube 46 is conducting current, the reactance of the output Windingof the reactor 48 is reduced; to a low value so that current passes readily from the power line through the conductor 53, the output winding of the reactor 48, the motor windingjfl and the conductor 56 to the other side of the power line. Current also passes from thejoutput winding of the reactor 48 through the condenser 58 and the motor winding 55 to the other side'of the power line. The condenser will cause the phase of the current in Winding 55 to lead that of the current in the winding 54, and the motor will rotate in one direction. A reversal in phase of the amplifier output will cause the portion of the motor control circuit, including the reactor 49 and the tube 41, to permit current flow from the power transformer. The reactance of the output'winding of the reactor 49 will then be reduced so that current will flow from the'power line directly through the motor winding55, and throughv the condenser 58 to the winding 54. The phase of the current in winding. 54 will then'lead that of winding 55, and the motor will rotate'in will position the contact so as to bring the poten-.

tial E4 to a value more nearly equal to the potential Ea. When the potentials E3 and E4 become equal, the grid 42 of the amplifier is no longer subjected to a potential, and the output of the amplifier becomes zero so that the motor '38 is no longer energized. If the core member I l and the contact 32 are moved together or separately to produce a potential E3 exceeding the potential E4, then the phase of the potential subjected on the grid of the amplifier will be such as to effect an operation of the motor in a direction-to in.- crease the potential E4. Movement of the core member H or the contact 32 to positions which amplifier and an energi'zation' oi the' inotor to position the contact 3I so as to reduce the potentialv E4. The, positioning of the contact 3| by the motor in either case will be indicative of the prod not of the values or conditions which caused the core member If and the contact 32 to assume the positions determining the position of the contact 3|.

In order that a visual indication or a record of the product of such values may be had, an indicator or pen arm is operatively connected to the motor 38 and is arranged to cooperate with a chart GI and an indicating scale 52.

It will be appreciated that the core member II and the contact 32 may be positioned by any means other than that shown responsive to the variable conditions to be measured, and the potential across the balancing potentiometer 24 could as well be produced by other means and froma source different from that producin the potential changes to be measured. I

In Fig. 2 'I have shown a transformer having a primary winding connected to a suitable source of A.-C., and bucking secondary windings 66 and 51 connected acros a potentiometer 58.

A core memberEQ magnetically couples the transformer windings and is adapted to be positioned by any variable condition. A balancing transformer I'll has a primary winding ll connected to a source of A.C., and a pair of bucking secondary 5;

winding 12 and 13 magnetically coupled to the primary winding by a core. member '14 which is operatively connected to the motor 38. A conductor T5 connects one end of the potentiometer 58 to one end of the bucking secondary windings, and the other, end of the secondary windings and a contact 16' movable along the potentiometer 58 by any variable, are connected to an amplifier and motor control. 17, similar to that of Fig. 1, by conductors T8 and 79, respectively. p

The potential across the portion of the potentiometer 68 between the contact l5 and the conductor 15' opposes the potential across the bucking secondary windings T2 and 13. When the potentials are unequal, the motor 38 operates to position the core member 74 until the potential across the secondary windings eouals that across the portionof the potentiometer .68. The position of the core member 14 when the system. is balanced, or the position of any suitable indicating means as shown in Fig. 1, indicates the product of the variables positioning the core member 59 andthe contact 16. If desired, the core member 69 or the contact I6 may be positioned manually .to establish a factor by which the variable positioning the other element is to be multiplied.

Fig. 3 shows a system like that of Fig". 2 except that a transformer is provided in place of the potentiometer fill. This transformer has a primary winding 8i connected to the ends of the secondary winding 56, 51, and bucking secondary windings 82 and 83 connected. at opposite ends to the conductor [5 and 19 leading, respectively, to one end of the buckin secondary windings l2, l3

and to the amplifier IT. A core member 85 mag- .3;

The flow meters is' supplanted, in 'Fig.'-4',' byis. conventional type of differential, mechanical motion meter-which gives a linear response with respect to flow. As diagrammatically depicted, meter I 00 moves the contact of potentiometer I'flI whose resistance is energized by the constant potential output of the dual-purpose movable core transformer I02. The output oi potentiometer l OI energizes potentiometer I03 whose contact is actuated from pressure as in Fig. l and the output of I03 is balanced by the varied output of I02 'to indicate the product of the values, or conditions, of flow and pressure.

The result attained by the system of Fig. 4 is similar to that attained by Fig. 1 but the altered combination with the novel movable core transformer emphasizes the flexibility of this device in a balanceable network. The position of the transformer in the system of Fig. 1 is, in one sense, reversed by the Fig. 4 disclosure.

Proceeding to a more detailed explanation of the function of the system of Fig. 4 it is to be noted that transformer I 02 includes, actually, two secondary windings in each of the two sets. This more fully explains the generation of E1 to be produced by the windings I04 and I05 connected in aiding relation to each other, as their adjacent arrows indicate. Secondary windings I06 and I01, are connected bucking as are windings I1 and I8 of Fig. 1 and when the core assumes a central position relative to the windings the resultant induced potential in these windings is equal to zero. A movement of the core from its central position results in an increase in the potential induced in one of the windings I06, I07 and a decrease in the potential induced in the other winding. The resultant potential across these windings will then be equal to the value E2 which is dependent upon the distance at which the core is spaced from its neutral position. 4

With theconstant potential at impressed across the resistance or Mil, the portion of the potential E1 selected by meter I 00 in its positioning of the contactor of Hi! (E3) is impressed across the resistance of iii-3. The contactor of I03 is then positioned by the pressure responsive device to select a portion of the output potential of IIlI as 134 for comparison with the variable output potentia1 of the winding I06, I 0T of transformer I02.

As in Fig. 1. the potential outputs of H33 and )2 are brought together in an amplifier'section similar to 35. This amplifier is'a well known electronic type including a double triode electron tube, preferably of the 6SL7 type. A departure of the potentialoutputs of H32 and IE3 from equality establishes a potential as" on the amplifier of. one phase or the other, depending upon which of the outputs is the greater, and of a magnitude dependent upon the amount by which they differ.

The motor control circuit disclosed in Fig. 4 is structurally quite different from that of Fig.1 although directed to the same function of sensing the phase of the output of the amplifier and corn secuently the unbalance of the measuring circuit for eubseouently operating the motor which will position the core of movable core transformer I02 to rebalance the measuring circuit. The control circuit consists of a sin'- gle tube Iii preferably of the high Gm or mutual conductance type, such as the GAG'I. This tube is connected in. series with the control winding II I of the motor H2. The plate current for the tube i It is unfiltered'pulsating D.-C. current obtained from a full wave rectifier tube N3 of the 6X5 type, receiving its power from a transformer II4 connected to the alternating current power source for the entire system. The potential output of the amplifier, produced by an unbalance of the measuring circuit, is applied to .the grid of the motor control tub H0. This potential, applied to the control grid, will cause an increase in the no-load plate current during the half-cycle when it is in phase with the plate current and a decrease during the half-cycle it is out of phase. As a result, with the large grid signal, half Wave pulses of D.-C. current will flow into the motor circuit comprised of the control winding III and the capacitor IIE in parallel. .The phase of this pulsating current depends on the phase of the grid signal which is E5 amplified.

The motor H2 is, in efiect, a two-phase motor which may be described as being a capacitorrun induction motor having a two-phase stator winding and a high resistance squirre1 cage type rotor. There are two identical but separate windings III, 5, the capacitor I I'i' being connected in series with a capacitor II6 across the A.-C.,power line so that voltage drop EMz, leads the line potential by nearly 90. The capacitor II! is chosen so that it is in resonance with the inductance of the winding H6 at the operating frequency and forms a series resonance circuit. This results in a voltage drop across the winding I I6 which is approximately double the line pocontrol winding, while identical with the first winding I I 6 in construction, difiers in that it has a capacitor H5 connected in parallel across it. The capacitor H5 is designed to produce a condition of parallel resonance at 60 cycles. The plate of the motor control tube H is always positive. At balance, some current flows during eachhalf cycle, but since this current is only slightly pulsating direct current and has no fundamental component of supply line frequency, no output torque on the motor is produced. Any tendency of the motor to coast is restrained by the dampening action of the D.-C. component which applies a braking action. As balance is approached from an unbalanced condition, there results a reduction in the fundamental component of supply line frequency in the output circuit of tube I I0, and a consequent and simultaneous increase in the D.-C. component which produces a dynamic braking action and prevents over-travel.

When the measuring circuit is unbalanced, half-wave pulsating current which flows from the motor control tube H0 into the winding I II and capacitor H has a large fundamental 60 cycle component retaining, as well, higher frequency harmonic components and the D.-C. component which gives the braking action upon motor rotation. However, this parallel circuit is tuned so that the capacitor H5 is in resonance with the winding III inductance for 60 cycles. This produces a large A.-C. voltage drop EM1 of 60 cycle frequency across the motor winding I I I, but reduces the harmonics to a minimum since the parallel resonance circuit acts like a very high impedance to 60 cycle current, but a relatively low impedance to harmonics. In this arrangement the motor tube current may be only 12 milliamps with 30 milliamps or more alternating current in the control winding II I. This A.-C. control winding voltage drop lags or leads the main winding I I6 potential by approximately depending on the phase of the control tube I I0, grid potential and direction of unbalance of the measuring circuit. Consequently, the motor H2 will run as a two-phase motor in a direction determined by the phase relationship by the winding voltage drops and rebalance the circuit by actuation of the core of movable core transformer I02.

The motor is of a low inertia rotor type havin high impedance windings. The speed of response of the motor to amplifier signal is far higher than the system of Fig. 1 because of the low motor inertia and the absence of time lag in the motor control circuit. Stability is obtained with total travel time of full scal indicator or recorder operation of approximately one second, and with the sensitivity of one-tenth percent or better. At this speed of travel and sensitivity, a sudden change in the input signal will produce a single cycle of overshoot or one percent maximum.

This motor control circuit is described in even more detail in my Patent 2,544,790.

It can thus be seen that the system described in Fig. 4 provides a balanceable network which may be unbalanced in one direction or another by variations in either or both of the two conditions, flow and pressure, of the fluid in theconduit disclosed. When the balance of the network is disturbed, its potential output E5 is of a phase and magnitude representative of the direction and extent of network unbalance. Such output E5, applied to the amplifier, produces an amplified -A.-C. signal E5 of phase and magnitude representive of network unbalance which is applied to the motor control, resulting in rotation of the motor I I2 in one direction or the other dependent upon the direction of unbalance. Such motor rotationis in proper direction to position the core of movable core transformer I02 to rebalance the network and decrease the output E5 to zero. As the system approaches balance, considerable braking action is effective on the rotor, which reduces the tendency to over-travel and hunting.

Simultaneously with the positioning of the movable core transformer I 02 the motor I I2 positions the indicator an amount representative of the product of the flow and pressure.

Coming now to Fig. 5 I disclose for thefirst time, in connection with a balanceable network of the types found in Figs. 1 and 4, a responsive device which varies a voltage output without resort to mechanical actuation. In short, a Wheatstone bridge is arranged sensitive to the temperature condition of the fluid flowing in the disclosed conduit. This bridge I20, although adjacent the point at which the measurement is taken, may be given its basic potential supply from the secondary windings I04, I05 of movable core transformer I02, which is located at a comparatively remote point of recordation and/or control action with respect to the fluid of the conduit. The output potential of bridge I20 is similar to that of potentiometer IOI of Fig. 4 in that it in turn energizes potentiometer I 2|, responsive to flow of the fluid. I

The balancing of the Fig. 5 system proceeds as in Fig. 4 but without mechanical actuation within, or of, responsivedevice I20. This association of the novel movable core transformer I02 again illustrates the broad application permissible with the device in any system wherein the base-loading, or energizing, potential of the responsive elements is desirably emanated from a single location. Whether the responsive elements arelo- 9 cateclv adjacent the point of recordation and/or control, or are separated therefrom by substantial distance, whether thepotential delivering devices are mechanically actuated from the variable orlinhfirently respond to the varial ile, or whether the base lcading potential structure to be located at the transmitteror receiver, my. novel transformer usefulin reducing the number of transformer devices required for energization and inproviding these functions in any desired combina I .I 5 Fig 6 I have disclosed a-relatively simple combination of 'a sensitive bridge balanced against my novel, dual-purpose movable core transformer output. More commonly,lin the past, it has been the practice to either vary an opposing resistance leg of a Wheatstone bridge untila balance is attained or to allow thebridge tore main unbalanced, with its output across a loadresistance. ,I now propose, with my. dua1- purpose movable core transformer, to allow the bridge to :remainunbalanced with its output across a load resistance, but to oppose the output across this load resistance with the variable output of my novel transformer. I have specifically disclosed this in the. structure cf the bucking sets of secondaries simultaneously opposing the bridge I output across resistance 13!. The core transformer 592 is positioned by cam l32.a s a link with motor I33 which is driving it, until the secondary a potential equals the bridge potential.

"The difference, in phase and magnitude, between the potentials at any one time is'sensed by the amplifier its inseries with the bridgeoutput and resistor Isl, and the motor I33 responds, to

reduce this diiference by actuating cam 32 to position the core-oi transformer 102.

Motor l33 can be easily arranged to not only actuate cam I32 but simultaneously actuate an indicating-and/or recording device :35 aswell as aipotentiometer 13tincorporated in a teleme'tering circuit, not shown, transmitting the motion as a value of the variable temperature to a remote position of recordation and/or indication and possibly control of the variable.

Fig. 6, in contrast to the elongated system to Fig. 5, is conceived as a compact, unified, combination of the temperature measuring instrument. The novel movable core transformer is useful in either combination. In either embodiment, the conventional balancing potentiometer is superseded by my novel movable core transformer which is more suitable for operating in corrosive or explosive atmospheres because of the elimination of exposed contacts and slidewires.

While I have described several forms which my invention may assume in practice, it will be understood that the invention is not limited to these forms but may be modified and embodied in various other forms without departing from the spirit or the scope of the appended claims.

This application is a continuation-in-part of my application Serial No. 731,465, filed February 28, 1947, now abandoned.

What I claim as new, and desire to secure by Letters Patent of the United States, is:

1. A measuring network including, in combination; a transformer having a primary winding, a first secondary winding structure, and a second secondary winding structure including a. pair of bucking secondary windings; a source of alternating current potential for the primary winding; a core member for varying the potential induced in the bucking secondary windings while producing no total effect on the potential induced in the first secondary winding structure; means for positioning the core in response to changes in a variable; a potentiometer connected across the first secondary winding structure and having a movable contact; means for connecting the potentials between the ends of the second secondary winding structure and one end of the potentiometer and its contact in opposition; and means responsive to any diiierence between said potentials for operating the contact to balance the potentials.

2'. A calculating network comprising, in combination, a tranfsormer having a primary winding, 2. single'secondary winding, and a pair of bucking secondary windings, means for connecting said primary winding to a source of alternating current potential, a core member magnetically coupling said primary winding to said secondary windings and movable relative thereto so as to vary the potentials induced in the bucking secondary windings and to produce no effect on the potential induced in the single secondary winding, means for moving said core member in response to changes in the variable, a potentiometer connected across said bucking secondary windings and having a movable contact, means for moving said contact in response to changes in a second variable, a potentiometer connected across said single secondary winding and having a movable contact, means for connecting the potentials between one end of each of said potentiometers and their contacts in opposition to each other, and means responsive to any difierence between said potentials and operative to position the contact for said second mentioned potentiometer in a direction to balance the p0- tentials.

3. The calculating network of claim 2 in which the means responsive to differences between potentials is an electronic amplifier having a pair ofoutput tubes selectively energized in accordance with the phase of said difference, a motor for operating the contact for said second potentiometer and means dependent upon the tube energized to control the direction of motor operation.

4. A measuring network including, in combination; a transformer having a primary winding, a first secondary winding structure, and a second secondary winding structure including a pair of bucking secondary windings; a source of alternating current for the primary winding; 2. core member for varying the potentials induced in the bucking secondary windings while not producing any variation in the total potential induced in the first secondary winding structure; a variable potential delivering means connected across the first secondary winding structure; means for connecting the potentials across the second secondary winding structure and the variable potential delivering means in opposition; and means responsive to any difference between said potentials adapted to vary one of the potentials to bring them to equality.

5. A measuring network including, in combination, a device delivering a potential in accordance with a variable, a movable core transformer with a pair of bucking secondaries anda pair of aiding secondaries providing a dual output, means for arranging the aiding secondaries to energize the device delivering the variable potential, means for arranging the output of the bucking secondaries to oppose the output of the device delivering the variable potential, means responsive to the difference between the output 11 0f the, bucking secondaries and output'ofth'e device delivering the variable potential, actuating means for the movable core transformer contransformer with a pair of bucking secondaries and a pair of aiding secondaries providing a dual output, the aiding secondaries energizing the first device and the bucking secondaries opposing the output voltage of the second device; and means responsive to any difierence between the opposed voltages and operative to position the core in a direction to balance the potentials.

'7. The network of claim 6 in which the means responsive to difierences between the opposed potentials is an electronic amplifier sensitive to the phase of the difference, a motor for operating the movable core transformer core and means dependent upon the amplifier output to control the direction of motor operation.

8. A measuring network including, in combination, a Wheatstone bridge sensitive to a temperature condition and delivering a potential output in accordance with the value of the temperature; a movable core transformer with a dual set of secondary windings, one of the set arranged to energize the bridge, and the other set arranged to oppose the bridge output; a device sensitive to difierence between the opposed outputs of-bridge and transformer; and means controlled by the sensitive device to actuate the yariable and the energization; a movable core transformer core toward reduction of the dif- Ierence.

4 9.. A balanceable network including; a transformer having a primary winding energized to form a source of alternating current potential, 2. first secondary winding structure, a'second secondary winding structure comprising a pair of bucking secondary windings, and a core member for varying the potentials induced in the bucking secondary windings while producing substantially no variation in the total potential induced in the first secondary winding structure; means introducing the output of the second secondary windings into the network; a first device enerized by the potential of the first secondary winding and introducing its output into the net- I work; a-- second device energized from thesec- 0nd secondary windings of the transformer and introducing its output into the network; means i for varying the output of one device into the network by a variable; and means responsive to theunbalance of potentials in the network and adapted to vary the output of the other device into the network to balance the network.

ANTHONY J. HORNFECK.

' Referenc s Cited in the file or this patent UNITED STATES PATENTS Number Name Date I 1,960,350 Shackleton May 29, 1984 2,208,623 Bond July 23, 1940 2,346,838 Haight Apr. 18, 1944 2,406,221 Hornfeck Aug. 20, 19.46 2,439,891 Hornfeck Apr. 20,1948

FOREIGN PATENTS Number Country v Date 553,947 Great Britain June 11, 1943 722,351, France May 16, 1932 

